LARGER FORAMINIFERAL BIOFACIES OF THE OCALA LIMESTONE

Larger benthic foraminifera (LBF) are used to examine three interrelated questions regarding the interpretation of the Mid-Late Eocene Ocala Limestone of Florida and southern Georgia (Florida Platform): (1) paleoenvironments (restricted or open shelf?); (2) morphology of the northern margin of the Florida Platform (rimmed shelf or ramp profile?); and (3) response of the platform during the terminal Eocene highstand (keep-up or drowned?).

Within the Ocala, the following LBF assemblages can be recognized: (a) Fallotella, Discorinopsis, and Lituonella in chloralgal/miliolid grainstones (Inglis Member, late Middle Eocene), representing shallow subtidal facies on a restricted platform; (b) small- to medium-sized Nummulites spp. (N. heilprini, N. willcoxi) with abundant miliolids, common Amphistegina, but rare Lepidocyclina in packstones and grainstones (Williston and lower Crystal River Members, Late Eocene), representing inner- to mid-ramp buildups; (c) Nummulites spp. and Lepidocyclina packstones (Crystal River Member), representing deeper photic zone buildups; and (d) Nummulites (esp. N. floridanus) and Lepidocyclina with common Pseudophragmina and Asterocyclina in packstones or grainstones (upper Crystal River Member), representing outer ramp deposits.

Ocala LBF therefore indicate restricted bank environments over the Florida Platform in the late Middle Eocene, but open shelf (ramp) conditions for the remainder of the Eocene. Sedimentation was transgressive and (in part) cyclical, with gradational biofacies changes upsection into the deeper photic zone. LBF shoal formation, however, was evidently possible anywhere along the transect, as seen in textulariid LBF grainstones, nummulitic coquinas, and even gypsum-cemented Lepidocyclina grainstones. The latter facies is found along the northern flank of the Florida Platform, adjacent to the current-swept Gulf Trough in the Crystal River Member, and probably indicates a distally-steepened ramp profile during the Late Eocene highstand.